#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
int frog(int steps);
int main()
{
	int steps;
	scanf("%d", &steps);
	printf("%d", frog(steps));
	return 0;
}
int frog(int steps)
{
	if (steps == 1)
		return 1;
	if (steps == 2)
		return 2;
	return frog(steps - 1) + frog(steps - 2);
}